1. Field of the Invention
The present invention relates to an internal combustion engine that has a dual lubricating oil circulation passage.
2. Description of the Related Art
There is known an internal combustion engine having a dual lubricating oil circulation passage.
Such an internal combustion engine includes a cylinder block, a cylinder head, a cylinder head cover, an oil pan and a chain cover.
A cylinder bore is formed inside the cylinder block. A pistons is slidably provided in the cylinder bore.
The oil pan is connected to the bottom portion of the cylinder block. The lower space of the cylinder block and a crank shaft storage space, which is the interior space of the oil pan, are communicated with the cylinder bore. In addition, the crank shaft storage space stores a crank shaft that rotates in conjunction with the operation of the piston.
The cylinder head is connected to the upper portion of the cylinder block. The space defined by a recess formed in the bottom portion of the cylinder head, the cylinder bore, and the upper end surface of the piston constitutes a combustion chamber. An intake valve and an exhaust valve, both of which can move upward and downward, are provided inside the cylinder head. Additionally, an inlet port and an exhaust port, which communicate with the recess (the combustion chamber) and are opened and closed by the intake valve and the exhaust valve respectively, are formed in the cylinder head.
A camshaft storage space is formed inside the cylinder head. The camshaft storage space, whose top surface is opened, is independent from the recess (the combustion chamber), the inlet port and the exhaust port. In other words, the camshaft storage space does not communicate with the recess, the inlet port and the exhaust port.
A camshaft, which extends linearly and is rotatable about its own axis, is disposed in the camshaft storage space. A through-hole is formed through a chain cover adjacent wall that constitutes a part of the outer peripheral wall of the cylinder head. One end of the camshaft passes through this through-hole and protrudes out of the cylinder head. An oil seal is provided between the inner peripheral surface of the through-hole and the outer peripheral surface of the camshaft. This oil seal is in contact with the inner peripheral surface of the through-hole and the outer peripheral surface of the camshaft in an air-tight and water-tight manner.
As is well known, both the intake valve and the exhaust valve are interlocked with the camshaft. Namely, when the camshaft rotates, the intake valve and the exhaust valve operate to open and close the inlet port and the exhaust port, respectively.
The cylinder head cover is fixed to the top surface of the cylinder head. Namely, the top surface of the cylinder head is covered with the cylinder head cover.
The chain cover is fixed to the cylinder block, the cylinder head, and the oil pan.
A chain storage space is formed inside the chain cover. This chain storage space communicates with the crank shaft storage space of the oil pan. On the other hand, the chain storage space does not communicate with the camshaft storage space. Namely, the chain cover adjacent wall of the cylinder head separates the camshaft storage space from the chain storage space in an in-air-tight and water-tight manner.
The one end of the camshaft, which passes through the through-hole of the chain cover adjacent wall, is located in the chain storage space. A timing chain, which is arranged in both the chain storage space and the interior space of the oil pan, is wounded around a sprocket provided at one end of the camshaft and a sprocket provided at one end of the crank shaft. Namely, the crank shaft and the camshaft are interlocked by the timing chain so that the camshaft is rotated by the rotational force of the crank shaft.
The crank shaft storage space of the oil pan is filled with a first lubricating oil.
In addition, the crank shaft storage space is equipped with a first oil pump to circulate the first lubricating oil through the crank shaft storage space, the interior space of the cylinder block, and the chain storage space. Namely, a first lubricating oil circulation passage is formed so as to pass through the crank shaft storage space, the interior space of the cylinder block, and the chain storage space.
On the other hand, a sub oil pan, which communicates with the camshaft storage space, is formed in the cylinder head. The sub oil pan is filled with a second lubricating oil.
In addition, the camshaft storage space is equipped with a second oil pump to circulate the second lubricating oil through the sub oil pan and the camshaft storage space. Namely, a second lubricating oil circulation passage is formed so as pass through the sub oil pan and the camshaft storage space.
Then, when the first oil pump is operated, the first lubricating oil circulates through the first lubricating oil circulation passage, and when the second oil pump is operated, the second lubricating oil circulates through the second lubricating oil circulation passage.
The first lubricating oil circulating through the first lubricating oil circulation passage enables the piston, the crank shaft, and the timing chain to operate smoothly. Furthermore, the second lubricating oil circulating through the second lubricating oil circulation passage enables the camshaft, the intake valve, and the exhaust valve to operate smoothly.
As described above, the camshaft storage space is independent from the recess (the combustion chamber) of the cylinder head, the inlet port, and the exhaust port. Additionally, the chain cover adjacent wall of the cylinder head separates the camshaft storage space from the chain storage space in an air-tight and water-tight manner.
Therefore, the first lubricating oil circulation passage and the second lubricating oil circulation passage are independent from each other. In other words, the first lubricating oil does not flow into the second lubricating oil circulation passage and the second lubricating oil does not flow into the first lubricating oil circulation passage.
By the way, when the internal combustion engine operates, so-called blowby gas is generated in the combustion chamber. This blowby gas flows through the gap between the inner circumferential surface of the cylinder bore and the end gap of the piston ring attached to the piston, and flows into the crank shaft storage space. The blowby gas comes in contact with the first lubricating oil, and then the first lubricating oil deteriorates. Then, the first lubricating oil needs to be replaced with new lubricating oil with a certain frequency.
On the other hand, the recess (the combustion chamber) and the camshaft storage space are independent from each other. Then, the blowby gas does not flow into the camshaft storage space to come into contact with the second lubricating oil.
Additionally, since the chain cover adjacent wall separates the camshaft storage space from the chain storage space in an air-tight and water-tight manner, the blowby gas does not flow into the camshaft storage space from the chain storage space to come into contact with the second lubricating oil.
Therefore, the second lubricating oil is harder to deteriorate than the first lubricating oil. Then, the exchange frequency of the second lubricating oil with new lubricating oil is lower than that of the first lubricating oil.
It should be noted that Japanese Unexamined Patent Application Publication No. H08-246831 and Japanese Unexamined Patent Application Publication No. 2011-190721 disclose a background technology related to the present invention.